The invention relates to an energy absorber for motor vehicle bumpers with a number of stiffening elements arranged between a bumper bracket and a bumper shell of a bumper, wherein the stiffening elements have free-standing front sides facing away from a rear mounting structure that is capable of being fastened to the bumper bracket, and whose centers are also laterally offset from one another in the longitudinal direction.
Such an energy absorber for motor vehicle bumpers is known from U.S. Pat. No. 3,506,295. The known energy absorber is stamped out of flat stock and has raised portions projecting on both sides relative to a reference plane at regular intervals, which are offset relative to one another in the longitudinal direction of the bumper. The side edges of the raised portions are joined to one another at their points of intersection, while the crests of the raised portions are flattened and intended for attachment to a bumper shell and a bumper bracket. Attachment to the bumper bracket and bumper shell is accomplished such that the energy absorber can extend in a longitudinal direction in the event of a collision, wherein the energy is distributed very effectively over the entire length of the energy absorber by means of the joining points. While the known energy absorber does have the advantage that the energy is transmitted effectively to the energy absorber, especially in the case of a severe collision with a relatively large object, this does, however, have the effect in collisions with objects that are relatively small in the energy absorber""s transverse direction, as for example a human leg, of causing high accelerations on the relatively small object because of the relatively great stiffness of the energy absorber. This is particularly disadvantageous with regard to the greatest possible protection of pedestrians.
Another energy absorber is known from U.S. Pat. No. 3,843,182. This energy absorber has as stiffening elements a number of ribs that are oriented transverse to the longitudinal direction of a bumper bracket of a motor vehicle bumper. The ribs are joined together at their front ends facing away from the bumper bracket, and also at their edge sides, by means of a bumper shell which is manufactured as a single piece with the ribs, and are spaced away from the bumper bracket. Inserted between the ribs are block-like damping bodies. Although it is true that the connection of the ribs to one another prevents the bumper shell from buckling in a collision with a relatively small object because of the stabilization provided by a number of adjacent ribs in addition to the ribs located in the collision area, the amount of energy absorbed by the energy absorber is relatively small.
Known from DE 44 01 874 C1 is a damping element that can be placed between a bumper shell and a bumper bracket of a motor vehicle bumper and that has a rib structure, formed by two spring legs and a web connecting the spring legs, consisting of a longitudinal rib that extends in the bumper bracket""s longitudinal direction and a number of transverse ribs oriented perpendicular to the longitudinal rib. While this gridlike rib structure does have elastic deformability even at high collision speeds, the amount of energy absorbed in a collision with a relatively small object is very low as a result of the compound structure of longitudinal rib and transverse ribs.
Provided in an energy absorber for bumpers of motor vehicles are stiffening elements, which have free-standing front sides facing away from a rear mounting structure. The stiffening elements have in the longitudinal direction a lateral center-to-center distance from one another that corresponds to the standard dimensions of a human leg. Side faces of the stiffening elements which face one another are designed such that, in the event of collision with a leg, the stiffening elements are deformable independently of one another, and in the event of collision with an object larger than a leg, the stiffening elements engage one another at their side faces in a manner hindering deformation with an abrupt increase in the stiffness of the energy absorber. By this means, braking with a relatively low deceleration is achieved in a collision with the leg, whereas the energy absorber is adequately stiff in a collision with a larger object.
The object of the invention is to specify an energy absorber of the type mentioned at the outset that is characterized, firstly, by high energy absorption in collisions with objects the size of a human leg of standard dimensions, and secondly, by great stiffness in collisions with objects that are relatively large in comparison thereto.